1. Field of the Invention
The present invention relates to a recording-medium identification device for identifying the type of recording medium fed by analyzing the optical characteristic thereof.
2. Description of the Related Art
Hitherto, various kinds of recording devices such as copiers, facsimile machines, printers, and so forth, have been used to perform printing on recording mediums such as sheets of paper, plastic sheets for an overhead projector (hereinafter referred to as an OHP sheet), and so forth. These recording devices can establish the best printing mode according to the type of recording mediums. For example, an ink-jet printer can change its ink-jetting mode so as to form a suitable image according to the type of recording medium, such as a plain-paper sheet, a high-quality-paper sheet, the OHP sheet, and so forth. In the past, a user of the recording device usually would manually set the type of a recording medium. However, when the user performs the setting improperly or neglects to perform the setting because of its complex procedures, it is impossible for the user to perform printing properly according to the type of the recording medium. Therefore, for solving the above-described problems, techniques for adding a recording-medium identification device to identify the type of recording medium for the recording device have been introduced.
For example, the following two methods are among those which have been introduced to identify the type of recording medium. According to a first method, the type of a recording medium is identified by measuring the thickness of the recording medium. According to a second method, the type of a recording medium is identified by reflecting light off the print surface of the recording medium and observing the reflected light to identify the type of recording medium.
Japanese Patent Laid-Open No. 8-188322 discloses the above-described first method. According to this method, however, the print-surface condition of the recording medium cannot be measured directly. Therefore, it has been difficult to identify the print-surface condition with precision and determine the type of the recording medium.
Japanese Patent Laid-Open No. 10-198093 discloses the above-described second method. In this method, a light-emitting element and a reflected-light-receiving element are provided adjacent the print surface of the recording medium. The light applied on the recording medium is reflected by the print surface thereof, whereby the type of the recording medium is identified. In this case, the print-surface condition can be determined directly. However, it is difficult to determine the print-surface condition with precision using only two parameters, that is, the specularly reflected light and the diffusely reflected light that are observed. This problem occurs in the case where specularly reflected light and diffusely reflected light obtained by a first recording medium and those obtained by a second recording medium, the second recording medium being different from the first recording medium in type, are similar to one another.
Recording media such as the high-quality-paper sheets and the plain-paper sheets other than OHP or coated-paper sheets produce a small amount of specularly reflected light. Since it is difficult to differentiate between the high-quality-paper sheet and the plain-paper sheet according to the intensity and amount of diffusely reflected light obtained by these two paper-sheets, the differentiation is often performed improperly. Thus, it has been difficult to identify with precision the type of a recording medium according to the above-described methods.